Coupling of polymers made by cationic polymerization

ABSTRACT

A method for coupling a cationic polymer includes forming a reaction mixture of a cationic polymer and a bis(diphenylethylene). The reaction mixture is exposed to a temperature which causes the bis(diphenylethylene) to react with the cationic polymer, thereby coupling the cationic polymer. In another embodiment, the method includes forming a reaction mixture of an oxo-acid and a isopropenyl polyisobutylene. The reaction mixture is exposed to a temperature below about -30° C., whereby the oxo-acid reacts with isopropenyl polyisobutylene, thereby coupling the polymer.

RELATED APPLICATION

This application is a division of application Ser. No. 08/398,953 filedMar. 2, 1995 now U.S. Pat. No. 5,690,861, which is incorporated hereinby reference in its entirety.

BACKGROUND OF THE INVENTION

Polymers are formed from a wide variety of organic compounds. Further,they are employed in many commercial applications, some of which havevery specific requirements. For example, some uses demand polymermaterials of extremely high purity, or within a narrow molecular weightrange. Other applications, such as many industrial uses, employ polymersas reactants for further conversion to compositions having particularproperties. Additionally, some applications require particular polymerconfigurations, such as A-B-A type triblock copolymers, wherein onemonomeric repeat unit includes a second monomeric repeat unit at eitherend of a linear polymer.

However, polymerization reactions typically are difficult to control.Even at constant reaction conditions, resulting polymers commonly havebroad ranges of molecular weight. Further, during polymerization,polymer chains can undergo chain transfer and side reactions. Thesepolymer products consequently have a molecular structure which areill-defined and which do not allow the physical properties of thematerial to be manipulated, such as by application of heat, or bymechanical force, and which limit the potential of the polymer as areactant for production of related compounds.

One attempt to control the molecular weight ranges and molecularstructure of polymers has been to employ living polymerizations. Theseare polymerizations which proceed with the absence of termination andchain transfer. As a consequence, living polymerizations generally yieldpolymers with well defined structure, controlled molecular weight, andnarrow molecular weight distribution.

However, some manipulations of polymers which have been formed bycarbocationic living polymerization have not been readily obtained. Forexample, coupling of polymers formed by carbocationic polymerization hasgenerally been unachievable.

Therefore, a need exists for a method of coupling polymers formed bycarbocationic living polymerization.

SUMMARY OF THE INVENTION

The present invention relates to a method for coupling polymers made bycationic polymerization.

In one embodiment, a reaction mixture is formed of a cationic polymerand a bis(diphenylethylene) having the formula: ##STR1## wherein R₁includes at least one carbon, and R₂ and R₃ are hydrogen or alkylgroups. The reaction mixture is exposed to a temperature which causesthe bis(diphenylethylene) to react with the cationic polymer, therebycoupling the cationic polymer.

In another embodiment, a reaction mixture is formed of an oxo-acid andisopropenyl polyisobutylene. The reaction mixture is exposed to atemperature below about -30° C., whereby the oxo-acid reacts with theisopropenyl polyisobutylene, thereby coupling the isopropenylpolyisobutylene.

The present invention has many advantages. For example, asymmetrictelechelic polymers, which have been formed by carbocationicpolymerization, can be coupled. The resulting coupled telechelicpolymers are symmetric and have a controlled molecular weight and anarrow molecular weight distribution. An example of a polymer which canbe formed by the method of the invention is an A-B-A type triblockcopolymer which has been formed by coupling A-B type asymmetrictelechelic cationic polymers. Particular examples of coupled polymerswhich can be formed by the method of the invention include emulsifiers,compatibilizers, and thermoplastic elastomers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a series of gel-permeation chromatograph (GPC) plots ofpolyisobutylene coupled with bis 4-(1-phenylethenyl)phenyl!propane,which was formed by the method of the invention, and wherein the molarratio of polyisobutylene to bis 4-(1-phenylethenyl)phenyl!propane isabout 1:2.

FIG. 2 is a series of GPC plots of polyisobutylene coupled with bis4-(1-phenylethenyl)phenyl!propane, which was formed by the method of theinvention and wherein the molar ratio of polyisobutylene to bis4-(1-phenylethenyl)phenyl!propane is about 1:1.

FIG. 3 is a series of GPC plots of an isopropenyl polyisobutylenemacromer and of the coupled product, which was formed in the presence oftriflic acid according to the method of the invention.

FIG. 4 is another series of GPC plots of an isopropenyl polyisobutylenemacromer, and of the coupled product, which was formed in the presenceof triflic acid.

DETAILED DESCRIPTION OF THE INVENTION

The features and other details of the invention will now be moreparticularly described with reference to the accompanying tables andpointed out in the claims. It will be understood that the particularembodiments of the invention are shown by way of illustration and not aslimitations of the invention. The principle features of this inventioncan be employed in various embodiments without departing from the scopeof the invention.

This invention relates to a method for coupling cationic polymers. A"cationic polymer," as defined herein, means a polymer which includes anet positive charge at an end group of the polymer. "Coupling," asdefined herein, means chemically linking two polymer molecules togetherto form a single molecule.

In one embodiment, the method includes forming a reaction mixture of acationic polymer and a bis(diphenylethylene). The bis(diphenylethylene)has the following general empirical formula: ##STR2## The phenyl (Ph)groups can include substituents, such as alkyl, hydrogen, or otherfunctional groups. R₁ includes at least one carbon. R₂ and R₃ includehydrogen or alkyl groups. In a particularly preferred embodiment, thebis(diphenylethylene) is 2,2 bis 4-(1-phenylethenyl)phenyl!propaneBPEPP!, which has the following structural formula: ##STR3##

Generally, the cationic polymer is a telechelic asymmetric cationicpolymer. As defined herein, a "telechelic polymer" means a linearpolymer that is substituted with functional groups at both ends. Atelechelic polymer in which these functional substituents are differentis "asymmetric," while a "symmetric" telechelic polymer is one withidentical substituents at both ends. Embodiments of the presentinvention include both symmetric and asymmetric telechelic polymers.

Examples of suitable cationic polymers include those which are disclosedin copending U.S. application Ser. No. 08/173,493, the teachings ofwhich are incorporated herein in their entirety. Preferred examples ofsuitable cationic polymers include polyisobutylene (PIB) andpolystyrene. Further, the number of repeat units in the polyisobutyleneis generally greater than about two.

The reaction mixture of the cationic polymer and thebis(diphenylethylene) is exposed to a temperature which causes thebis(diphenylethylene) to react with the cationic polymer, therebycoupling the cationic polymer. Typically, the temperature to which thereaction mixture is exposed is in a range of between about -100° C. and0° C. Preferably the temperature is in a range of between about -100°and -30° C. In a particularly preferred embodiment, the temperature towhich the reaction mixture is exposed is about -80° C.

The molar ratio of the bis(diphenylethylene) to the cationic polymer issufficient to cause coupling of the cationic polymer at the temperatureto which the reaction mixture is exposed. In one embodiment the molarratio of the bis(diphenylethylene) to the cationic polymer is in therange of between about 1:1 and 1:2. Preferably the molar ratio of thebis(diphenylethylene) to the cationic polymer is about 1:2.

In one embodiment, the cationic polymer is a block copolymer. Forexample, the cationic polymer can be a diblock copolymer, wherebycoupling of the cationic polymer by the method of the invention causesformation of an A-B-A type triblock copolymer.

In a specific embodiment, the cationic polymer is a polyisobutylene andwherein the bis(diphenylethylene) is 2,2 bis4-(1-phenylethenyl)phenyl!propane. In this particular embodiment, thereaction mixture can include, in addition to the polyisobutylene and the2,2 bis 4-(1-phenylethenyl)phenyl!propane, methyl chloride and hexane asa solvent base, wherein the methyl chloride comprises about 40% byweight of the solvent base and hexane comprises about 60% of the solventbase. The overall mechanism of the reaction is believed to be asfollows: ##STR4##

The reaction period for coupling is sufficient to cause a substantialportion of the cationic polymers to couple. The resulting coupledcationic polymer can be separated from the reaction mixture by asuitable technique, such as by evaporation of the solvent, etc. If thecoupled cationic polymer is subsequently reacted with another reactant,such as methanol, the resulting reaction product can be separated by thesame method, or by some other suitable method.

In an alternate embodiment, the method includes forming a reactionmixture of an oxo-acid and isopropenyl polyisobutylene. The isopropenylpolyisobutylene has the following structural formula:

    PIB-CH.sub.2 --C(CH.sub.3)═CH.sub.2

Examples of suitable oxo-acids are triflic acid and perchloric acid. Apreferred oxo-acid is triflic acid.

Preferably the isopropenyl polyisobutylene has a repeating isobutyleneunit of at least two. In a particularly preferred embodiment, theisopropenyl polyisobutylene includes a repeating unit of at least aboutnine.

The reaction mixture is formed at a temperature below about -30° C.,whereby the oxo-acid reacts with the isopropenyl polyisobutylene,thereby coupling the isopropenyl polyisobutylene. In a specificembodiment, the reaction mixture is formed at a temperature below about-50° C. to cause coupling of the isopropenyl polyisobutylene.Preferably, the reaction mixture is formed at a temperature of about-80° C. The reaction mixture typically includes a relatively non-polarsolvent, such as hexane and a low concentration of acid. It is believedthat the following reaction products are formed: ##STR5##

The invention will now be further and more specifically described withregard to the following examples. All parts and percentages are byweight unless otherwise specified.

EXEMPLIFICATION A. Materials

2,2 Bis 4-(1-phenylethenyl)phenyl!propane (BPEPP) was obtained accordingto a procedure described by Tang, Lo and Bener (L. H. Tang, G. S. Lo, D.E. Bener, Macromolecules:11, 616, 1978). Finely powdered anhydrous AlCl₃(0.062 mole, 8.3 g), anhydrous CH₂ CL₂ (100 mL, distilled from P₂ O₅),and CH₃ COCl (0.052 mole, 3.73 mL) were cooled to -15° C. To thisstirred solution, 2,2-diphenylpropane (I) (0.022 mole) in 50 mL CH₂ Cl₂was added dropwise over 20 min. The temperature was maintained at -15°C. to -10° C. The mixture was stirred at -10° C. to +5° C. forapproximately 3 hours, then left standing at room temperature overnight.The resulting dark red solution was poured onto crushed ice, extractedwith CH₂ Cl₂, washed with water until neutral, dried over anhydrousMgSO₄ and filtered. The solvent was removed and 5.34 g (80%) ofcrystalline product 4,4'-diacetyl, 2,2-diphenyl-propane (II) wasobtained. Finally, the product was purified by recrystallization fromdiethylether.

PhMgBr (3M in ether, 0.23 mole) was cooled to -10° C. and (II) in 50 mLanhydrous benzene was added dropwise while stirring during 45 min. at-10° C. The mixture was stirred for 1 h, then poured onto a mixture of(100 g) crushed ice and (6 mL) concentrated H₂ SO₄. The organic layerwas separated, washed with water until neutral, dried over MgSO₄ andfiltered. The solvent was removed by a rotary evaporator at roomtemperature to give 6.5 g of 4,4'-bis(1-phenyl-1-hydroxyethyl)diphenylpropane (III) as a pale amber gum.

A solution of (III) (0.011 mole) in xylene (100 mL) containing 10 dropsof H₃ PO₄ was refluxed for 3 hours and the water formed during thereaction was collected in a Dean-Stark trap. The xylene was removed andthe product 2,2 bis 4-(1-phenylethenyl)phenyl!propane (IV) was dilutedwith cyclohexane. The solution was purified by flash chromatographyusing a 2 cm×15 cm of 100-200 mesh 60, a silica gel (commerciallyavailable from Aldrich, Inc.) column, and hexane as the eluent. Theeffluent was monitored by a short wave UV source and silica gel TLCplates containing fluorescent indicator. The sample was collected at thefirst sign of UV absorbing material being eluted from the column (thesample eluted between 150-200 mL). This effluent was collected andreduced to a viscous liquid by rotary evaporator. This chromatographystep was then repeated. The product was recrystallized from methanol,yield=80%, m.p.=80.6° C. The ¹ H NMR spectrum of the product exhibited amultiplet at 7.2 ppm (18 aromatic protons), a doublet at 5.4 ppm (4vinyl protons) and a triplet at 1.7 ppm (6 methyl protons).

B. Procedures

1. Synthesis of ω-isopropenyl-PIB

PIB carrying tert-chloro termini (PIB-Cl) was obtained using theTMPCl/BCl₃ /IB/DTBP/CH₃ Cl/-40° C. system. M_(n) ˜500 and 1000 polymerswith narrow molecular weight distribution were prepared.ω-isopropenyl-PIB was obtained by dehydrochlorination of PIB-Cl. J. P.Kennedy, V. Chang, R. A. Smith and B. Ivan, Polymer Bulletin: 1, 575(1979). A representative experiment was as follows: in a 500 mLErlenmeyer flask equipped with stirring bar and condenser 10 g of PIB-Cl(0.0213 mol), 23 g t-BuOK and 300 mL THF (refluxed overnight undernitrogen in the presence of Na-banzophenone) were added. The solutionwas refluxed for 20 hours and then cooled to room temperature.Subsequently, 150 mL n-hexane was added, stirred for a few minutes, 150mL distilled water and 50 mL methanol were introduced and stirred for 10minutes; the organic layer was washed with distilled water and driedwith anhydrous magnesium sulfate. Finally, the product was filtered andthe solvent was removed by rotavap and dried in vacuo.

2. Dimerization of PIB-CH₂ --C(CH₃)═CH₂

Isopropenyl polyisobutylene was dimerized, using hexane as a solvent,and in the presence of triflic acid at about -80° C.

3. Coupling by bis(diphenylethylene)

Isobutylene was polymerized by 2,4,4 trimethylpentylchloride (TMPCl) inconjunction with titanium tetrachloride (TiCl₄) in the presence ofditertiarybutylpyridine (DTBP) in methylchloride and hexane at avolume:volume ratio of 4:6 at -80° C. When the isobutylenepolymerization was complete, 2,2 bis 4-(1-phenylethenyl)-phenyl!propaneBPPEP! was added. At intervals thereafter, the reaction was quenched bythe addition of precooled methanol, and the reaction product wasisolated by evaporating the reaction solvents.

C. Results and Discussion

FIG. 1 shows GPC RI traces of PIB and the coupled product with BPEPP.Conditions: IB!=0.54M, 2,4,4 trimethylpentylchloride TMPCl!=3×10⁻² M,ditertiarybutylpyridine DTBP!=6×10⁻³ M, TiCl₄ !=1.2×10⁻¹ M,MeCl/Hexane-4/6 v/v, Temp.=-80° C., after 1 h polymerization time BPEPPwas added (0)-initial, M_(n) =1100, M_(w) /M_(n) =1.45. (8)-1 h.,BPEPP!/ TMPCl!=0.5, coupled product: M_(n) =2010, M_(w) /M_(n) =1.35.

According to the molecular weight of the products, diaddition of livingPIB to BPEPP is rapid and quantitative.

Close to quantitative coupling was also observed when the TMPCl!/MDDPE!=1 ratio was used as evidenced by size exclusion chromatography,presented in FIG. 2, which shows GPC RI traces of PIB and the coupledproduct with BPEPP. Conditions: IB!=0.54M, TMPCl!=3×10⁻² M, DTBP!=6×10⁻³M, TiCl₄ !=1.2×10⁻¹ M, MeCl/Hexane-4/6 v/v, Temp.=-80° C., after 1 hpolymerization time BPEPP was added (0)-initial, M_(n) =1100, M_(w)/M_(n) =1.45. (12)-1 h., BPEPP!/ TMPCl!=1, coupled product: M_(n) =2060,M_(w) /M_(n) =1.39.

For dimerization of PIB olefins, two samples of M_(n) =500 and M_(n)=1000 g/mol were used.

At -80° C., using low concentration of oxo-acid, dimerization of PIBmacromer proceeded and the extent of dimerization increased with time.

FIG. 3 shows GPC RI traces of the product obtained in the dimerizationwith triflic acid. PIB olefin!=0.4M, CF₃ SO₃ H!=10 mM, Temp.=-80° C.,solvent hexane, (0)-initial, Mn=1050 M_(w) /M_(n) =1.11, (7)-1.5 h.M_(n) =1600 M_(w) /M_(n) =1.28, (3)-2 h M_(n) =2180 M_(w) /M_(n) =1.06.

FIG. 4 shows GPC RI traces of the products dimerization with triflicacid PIB olefin!=0.5M, CF₃ SO₃ H!=10 mM, Temp.=-80° C., solvent hexane,(0)-initial, Mn=1050 M_(w) /M_(n) =1.11, (1)-0.5 h. M_(n) =1700 M_(w)/M_(n) =1.22, (3)-1.5 h M_(n) =2160 M_(w) /M_(n) =1.04.

The results demonstrate that quantitative dimerization of PIB olefin canbe achieved in a non-polar solvent at -80° C. by using 0.5M (completedimerization after 1.5 h) or 0.4M concentration (complete dimerizationafter 2 h).

EQUIVALENTS

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to the specificembodiments of the invention described specifically herein. Such areintended to be encompassed by the following claims.

I claim:
 1. A method for coupling an isopropenyl polyisobutylene,comprising the steps of:a) forming a reaction mixture of an oxo-acid andan isopropenyl polyisobutylene; and b) exposing the reaction mixture toa temperature below about -30° C., whereby the oxo-acid reacts with theisopropenyl polyisobutylene, thereby coupling said isopropenylpolyisobutylene.
 2. The method of claim 1, wherein the isopropenylpolyisobutylene includes greater than two isobutylene repeating units.3. The method of claim 2, wherein the isopropenyl polyisobutyleneincludes of at least about nine isobutylene repeating units.
 4. Themethod of claim 1, wherein the oxo-acid is triflic acid.
 5. The methodof claim 1, wherein the oxo-acid is perchloric acid.
 6. The method ofclaim 1 wherein the reaction mixture is exposed to a temperature belowabout -50° C.
 7. The method of claim 6 wherein the reaction mixture isexposed to a temperature of about -80° C.